1. Field of the Invention
The present invention relates to a convertor station for connection of a high-voltage DC line and an AC network, said station comprising a number of static convertors which are parallel-connected on the DC side as well as on the AC side. The station is provided with a regulator for setting a certain transmission magnitude between the DC and AC sides of the station, and each static convertor is provided with its own regulating circuit connected between said regulator and the proper static convertor, which is thus controlled from the regulator of the station.
2. The Prior Art
Such a convertor station occurs in DC power transmissions between different AC networks, each AC network being connected to the high-voltage DC line by way of a convertor station. To obtain the desired transmitted power it is common for each station to comprise several static convertors, the AC sides of which normally are connected in parallel with the AC network of the station, whereas the DC sides of the static convertors may be connected to the DC line in series or in parallel with each other. The present invention relates to the latter case and, as mentioned, the station is controlled by a regulator which normally receives a control order from a superior control system for the whole transmission for control of the load of the various stations.
In the case of parallel-connected convertors in one station, certain conditions should be fulfilled, the first condition being that the current order should normally be the same to all parallel convertors, while at the same time it should be possible to reduce the current order of a convertor to zero in order that the convertor may be disconnected. Furthermore, the total current order for the station and thus the actual current of the station should be independent of the fact that a convertor is disconnected.